Handoff of a mobile station between packet-switched and circuit-switched wireless domains

ABSTRACT

A first mobility management entity (MME) is configured to cooperate with a first access network controller to provide a circuit switched service to a mobile station while the mobile station is attached to a packet switched wireless access network in a first coverage area. A second MME is configured to cooperate with the first access network controller to provide a circuit switched service to the mobile station when the mobile station has moved from the first coverage area to the second coverage area. A home subscriber system is operated to provide, to the second MME, information identifying the first access network controller as serving the mobile station to enable the second MME to initiate handoff of the mobile station from the packet switched wireless access network to the circuit switched wireless access network.

CROSSED-REFERENCE TO RELATED APPLICATION

This Application is a Continuation of U.S. patent application Ser. No.13/666,197, filed Nov. 1, 2012, entitled “HANDOFF OF A MOBILE STATIONBETWEEN PACKET-SWITCHED AND CIRCUIT-SWITCHED WIRELESS DOMAINS”, which isa Continuation of U.S. patent application Ser. No. 12/831,496, filedJul. 7, 2010, now U.S. Pat. No. 8,320,334, issued Nov. 27, 2012,entitled “HANDOFF OF A MOBILE STATION BETWEEN PACKET-SWITCHED ANDCIRCUIT-SWITCHED WIRELESS DOMAINS”, the entire contents of all of whichare hereby incorporated herein by reference.

BACKGROUND

Various wireless access technologies have been proposed or implementedto enable mobile stations to perform communications with other mobilestations or with wired terminals coupled to wired networks. Examples ofwireless access technologies include GSM (Global System for Mobilecommunications) and UMTS (Universal Mobile Telecommunications System)technologies, defined by the Third Generation Partnership Project(3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies,defined by 3GPP2. CDMA 2000 defines one type of packet-switched wirelessaccess network, referred to as the HRPD (High Rate Packet Data) wirelessaccess network.

Another more recent standard that provides packet-switched wirelessaccess networks is the Long Term Evolution (LTE) standard from 3GPP,which seeks to enhance the UMTS technology. The LTE standard is alsoreferred to as the EUTRA (Evolved Universal Terrestrial Radio Access)standard. The EUTRA technology is considered to be fourth generation(4G) technology, to which wireless network operators are migrating toprovide enhanced services.

SUMMARY

A first mobility management entity associated with a packet-switchedwireless access network receives information associated with a mobilestation being served by the first mobility management entity, where theinformation identifies a serving generic access network controller forthe mobile station. The serving generic access network controller isused to provide a circuit-switched service to the mobile station whilethe mobile station is attached to the packet-switched wireless accessnetwork. The first mobility management entity initiates a handoff of themobile station from the packet-switched wireless access network to acircuit-switched wireless access network, where the circuit-switchedwireless access network is in a region served by a second generic accessnetwork controller different from the serving generic access networkcontroller. In performing the handoff, the first mobility managemententity uses the information to identify the serving generic accessnetwork controller to communicate handoff-related messaging to theserving generic access network controller to cause provision of thecircuit-switched service to be handed off from the serving genericaccess network controller to the second generic access networkcontroller.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are described with respect to the following figures:

FIG. 1 is a block diagram of an example arrangement includingpacket-switched and circuit-switched wireless access networks in whichsome embodiments can be incorporated;

FIGS. 2 and 3 illustrate transitioning of a mobile station betweendifferent areas of a communication network, according to someembodiments;

FIGS. 4 and 5 illustrate message flow diagrams according to someembodiments; and

FIG. 6 is a block diagram of an example arrangement of a communicationsnode according to some embodiments.

DETAILED DESCRIPTION

Wireless service operators are transitioning to packet-switched accesstechnologies such as the Long Term Evolution (LTE) technology. The LTEtechnology is also referred to as the EUTRA (Evolved UniversalTerrestrial Radio Access) technology. The EUTRA technology or standardis defined by the Third Generation Partnership Projection (3GPP).

With a packet-switched wireless access technology such as that providedby EUTRA, traditional circuit-switched services may no longer besupported. Examples of traditional circuit-switched services includecircuit-switched voice calls, short message services (SMS) (which allowstext communications between mobile stations), and so forth.

In some implementations, to enable the provision of circuit-switchedservices over a packet-switched wireless access network, such as an LTEwireless access network, a solution referred to asvoice-over-LTE-via-generic access network, or VoLGA, has been defined.The general concept is to connect circuit-switched infrastructure,including mobile switching centers (MSCs), to the EUTRA network using agateway. VoLGA is based on the 3GPP Generic Access Network (GAN)standard. The GAN standard is designed to extend mobile services over ageneric IP access network, such as WiFi networks. VoLGA extends the GANcapability to EUTRA packet-switched wireless access networks.

VoLGA specifications are published by the VoLGA forum. The GANarchitecture is described in 3GPP TS 43.318. Although reference is madeto particular standards or technologies, it is noted that techniquesaccording to some embodiments can be applied to other types oftechnologies or standards. Reference to “EUTRA” is intended to coverboth existing EUTRA standards as well as subsequent standards evolvedfrom the present standards. Similarly, reference to “VoLGA” standards isintended to cover both the existing VoLGA standards as well assubsequent standards evolved from VoLGA.

FIG. 1 is a block diagram of an example arrangement that supportscircuit-switched-over-EPS-via-GAN services. Providingcircuit-switched-over-EPS-via-GAN services allows a network to not haveto rely on Internet Protocol (IP) Multimedia (IMS) services, forexample. IMS services are packet-switched services. “EPS” or “Evolvedpacket system” refers to a system that supports packet-switched wirelessaccess networks. An example of an EPS system is an EUTRA network. Withthe arrangement of FIG. 1, circuit-switched services can be provided toa mobile station while the mobile station is attached to apacket-switched wireless access network, such as an EUTRA accessnetwork. In the example of FIG. 1, an EUTRA network 100 includes a basestation 102 that is able to wirelessly connect to a mobile station 104that is in a coverage area of the EUTRA network 100. In the EUTRAcontext, the base station 102 is referred to as an enhanced node B(eNodeB). A “base station” can perform one or more of the followingtasks: radio resource management, mobility management for managingmobility of mobile stations, routing of traffic, and so forth.Generally, the term “base station” can refer to a cellular network basestation or access point used in any type of wireless network, or anytype of wireless transmitter/receiver to communicate with mobilestations. The term “base station” can also encompass an associatedcontroller, such as a base station controller or the radio networkcontroller. It is contemplated that the term “base station” also refersto a femto base station or access point, a micro base station or accesspoint, or a pico base station or access point. A “mobile station” canrefer to a telephone handset, a portable computer, a personal digitalassistant (PDA), or an embedded device such as a health monitor, attackalarm, and so forth. A relay station has elements that act in a similarway to a base station, and elements that act in a similar way to a“mobile station.”

The base station 102 is connected to various components, including aserving gateway 106 and a mobility management entity (MME) 108. The MME108 is a control node for the EUTRA network 100. For example, the MME108 is responsible for mobile station tracking and paging procedures.The MME 108 is also responsible for choosing the serving gateway for amobile station at initial attach and at the time of handover. The MME108 can also be responsible for authenticating the user of a mobilestation. More generally, the term “mobility management entity” refers toany control node associated with a wireless access network that performsvarious control functions on behalf of mobile stations in the coveragearea of the wireless access network.

The serving gateway 106 routes bearer data packets. The serving gateway106 also acts as a mobility anchor for the mobile station duringhandovers between different access networks. The serving gateway 106 isconnected to a packet data network 110 that provides connectivitybetween the mobile station 104 and a packet data network 112 (e.g., theInternet, a network that provides various services, etc.).

Although just one base station 102, MME 108, serving gateway 106, andPND gateway 110 are depicted, it is noted that there can be additionalsuch nodes in the EUTRA network 100.

FIG. 1 also shows a circuit-switched network 120, which has a basestation 123 (to which a mobile station 121 can be wirelessly attached),a serving GPRS support node (SGSN 124), and an MSC (mobile switchingcenter) 126. Provision of circuit-switched services is controlled by theMSC 126. The MSC 126 is connected to a mobile voice network 128. Thecircuit-switched network 120 of FIG. 1 is according to a Global Systemfor Mobile (GSM) technology, as defined by 3GPP. In otherimplementations, the circuit-switched network 120 can be according toanother technology.

As depicted in the arrangement of FIG. 1, a generic access networkcontroller (GANC) 130 is provided. Provision of the GANC 130 allows forsupport of circuit-switched services over a packet-switched wirelessaccess network, such as for the mobile station 104 that is attached tothe packet-switched wireless access network. The GANC 130 can also bereferred to as a VANC (VoLGA access network controller) inimplementations using VoLGA.

FIG. 1 also depicts an authentication, authorization, and accounting(AAA) server 132, which is connected to the GANC 130. The AAA server 132is used for performing authentication, authorization, and accountingtasks with respect to mobile stations. In addition, FIG. 1 shows a homesubscriber server (HSS) 134 connected to the AAA server 132. The HSS 134stores subscriber profiles that define capabilities and otherinformation associated with mobile stations. The HSS 134 is connected tothe MME 108. The MME 108 is also connected to the GANC 130.

An interface between the MME 108 and the GANC 130 is referred to as anSv interface 136, where the Sv interface 136 is used to support handoffprocedures between packet-switched wireless access networks andcircuit-switched wireless access networks.

Also depicted in FIG. 1 is a Wm interface 138 between the AAA server 132and the GANC 130, where the Wm interface allows the GANC 130 toestablish a secure session with a mobile station. The Wm interface 138also allows for the indirect provision of information to the HSS 134 foridentifying a serving GANC to an MME, as discussed further below.

An interface between the AAA server 132 and the HSS 134 is an SWxinterface 133. The forwarding of information from an HSS to an MME isover an interface referred to as an S6a interface 140.

Although specific connections and interfaces, as well as specific nodes,are depicted in FIG. 1, it is noted that alternative embodiments can useother arrangements.

FIG. 2 illustrates a distributed arrangement that includes two GANcoverage areas 202 and 204 that are served by respective GANC 206 andGANC 208, respectively. A mobile station 232 that is attached to awireless access network in the GAN coverage area 202 is supported byGANC 206, whereas a mobile station that is attached to a wireless accessnetwork in the GAN coverage area 204 is supported by GANC 208.

Also, as depicted in FIG. 2, an MSC 210 serves mobile stations attachedto wireless access networks in the GAN coverage area 202, while anotherMSC 212 serves mobile stations attached to wireless access networks inthe GAN coverage area 204. As further illustrated in the example of FIG.2, a first MME 214 serves mobile stations attached to wireless accessnetworks in the GAN coverage area 202, while another MME 216 servesmobile stations attached to wireless access networks in the GAN coveragearea 204.

FIG. 2 also shows base stations (BS1, BS2) connected to the MSC 210, andBS3 connected to the MSC 212.

As depicted in the example of FIG. 2, a circuit-switched domain 220 isorganized into location areas LA1, LA2, and LA3. The location area LA1is served by BS1, while the location area LA2 is served by BS2. Thelocation area LA3 is served by BS3. The location areas LA1 and LA2 arein the GAN coverage area 202, while the location area LA3 is located inthe GAN coverage area 204.

A packet-switched domain 222 (or more specifically in some examples, anEUTRA domain) is organized into tracking areas TA1, TA2, and TA3, whereTA1 and TA2 are served by MME 214, and TA3 is served by MME 216. Thetracking areas TA1 and TA2 are located in the GAN coverage area 202 andthe tracking area TA3 is located in GAN coverage area 204. FIG. 2 alsoshows a serving gateway 224 and PDN gateway 226 that is associated withMME 214, and a serving gateway 227 and PDN 228 associated with MME 216.

When the mobile station 232 is attached to an EUTRA access network, andthe mobile station is provided with circuit-switched services over EPS(e.g., the EUTRA access network), the mobile station is led by the EUTRAaccess network towards the geographically closest GANC (in other words,the GANC serving the GAN coverage area where the mobile station iscurrently attached). For example, when the mobile station 232 isattached to an EUTRA access network in tracking area TA1, the mobilestation is provided with circuit-switched services by GANC 206, sinceTA1 is in the GAN coverage area 202 associated with GANC 206.

Due to mobility, it is possible that the mobile station 232 can movebetween different GAN coverage areas, as indicated by arrow 230 in FIG.2, for example (between GAN coverage area 202 and GAN coverage area204). Even though the mobile station has transitioned between differentGAN coverage areas, the mobile station maintains its association withthe original serving GANC (e.g., GANC 206). Thus, in the example of FIG.2, when the mobile station 232 is originally in the GAN coverage area202, the mobile station 232 is served by GANC 206. After transitioning(230) from GAN coverage area 202 to GAN coverage area 204, the mobilestation 232 continues to be served by GANC 206, even though the GANcoverage area 204 is associated with GANC 208.

A mobile station registered to GANC 206 is served by MSC 210. When themobile station 232 transitions from EUTRA tracking area TA2 to EUTRAtracking area TA3, the mobile station 232 is handed off from MME 214 toMME 216 (in other words, the active context for the mobile station istransferred from MME 214 to MME 216). Note that the GANC has to be ableto accept connections from any MME in a particular region.

As further shown in FIG. 3, assuming that the mobile station 232 isoriginally attached to tracking area TA1 of the EUTRA domain 222, a path302 depicts the provision of circuit-switched services by the MSC 210 tothe mobile station 232 through the serving gateway 224, PDN gateway 226,and GANC 206.

Assuming that the mobile station 232 has ultimately transitioned totracking area TA3 of the EUTRA domain 222, a path 304 depicts theprovision of circuit-switched services by the original MSC 210 to themobile station 232 after transitioning to TA3. Note that although mobilestation 232 in tracking area TA3 is now in the second GAN coverage area204 (see FIG. 2), the mobile station 232 is still provided withcircuit-switched services by the original serving GANC 206. Note thatthe mobile station 232 when in the tracking area 283 is served by theMME 216.

It is also possible that the mobile station can further transition fromthe EUTRA domain 222 (e.g., TA3) to the circuit-switched domain 220 (tolocation area LA3 in the example of FIG. 3). This transition isindicated by arrow 306 in FIG. 3. To handoff the mobile station to thecircuit-switched domain 220, the handoff request from the MME 216associated with TA3 has to be forwarded to the original serving GANC206, and not to the GANC 208 that is associated with GAN coverage area204 in which TA3 is located. Sending a handoff request from MME 216 toGANC 208 would result in an error, since GANC 208 is not currentlyserving the call session for the mobile station 232.

Without techniques according to some embodiments, the MME 216 would haveno ability to find the correct GANC for sending the handoff request.Techniques according to some embodiments specify that a mobile stationis to perform a re-authentication procedure whenever the mobile stationre-registers to a GANC. Such an authentication procedure is executed viathe Wm interface between a GANC and an AAA server, such as the Wminterface 138 shown in FIG. 1. Information relating to theauthentication procedure is provided from the AAA server 132 to the HSS134, over the SWx interface 133. The information passed from the AAAserver 132 to the HSS 134 as part of the authentication procedureincludes an identity of the serving GANC, which can be an IP (InternetProtocol) address, a fully qualified domain name (FQDN), or some othertype of identifier.

As depicted in FIG. 4, the authentication procedure performed by themobile station is represented as 402. The information sent from the AAAserver to the HSS is represented as 404. Assuming that the mobilestation originally performs a registration procedure with the GANC 206while the mobile station is in a tracking area (TA1 or TA2) of the GANcoverage area 202, then the information sent from the AAA server to theHSS as part of the authentication procedure would include an identity ofthe serving GANC 206.

The HSS sends (at 406) the identity of the serving GANC to the servingMME, such as over the S6a interface 140 shown in FIG. 1 between the HSSand the MME. For example, when the mobile station 232 is in eithertracking area TA1 or TA2, and served by the MME 214, the identity of theserving GANC is sent from the HSS to the serving MME 214. Upon MMErelocation (408), resulting from a mobile station transitioning betweendifferent tracking areas of the EUTRA domain that causes the activecontext to be transferred from the serving MME to a target MME, theserving MME sends (at 410) the serving GAN identifier to the target MME.For example, if the mobile station transitions from tracking area TA2 totracking area TA3, then the mobile station is relocated from MME 214 toMME 216, which causes the active context associated with the mobilestation to be transferred from MME 214 to MME 216.

When in idle mode, a mobile station is to re-register and perform alocation update upon any significant change in location of the mobilestation to ensure a current MSC-MME-GANC binding. A “significant changein location” can refer to the location of the mobile station satisfyingsome criterion, such as being served by a different base station,movement by greater than some predefined distance, and so forth. Forexample, the re-registration performed by the mobile station can betriggered by the mobile station crossing a tracking area boundary withinthe EUTRA domain.

FIG. 5 depicts a simplified message flow diagram of a handoff betweendifferent GANCs resulting from a packet-switcheddomain-to-circuit-switched domain transition, such as the transitiondepicted by arrow 306 in FIG. 3. The current serving MME sends (at 502)a relocation request to the current serving GANC, as identified by theserving GAN identifier that is maintained by the current serving MME.Note that the current serving MME can be either the serving MME or thetarget MME depicted in FIG. 4. In response to the relocation request,the current serving GANC sends a relocation response (at 504) back tothe current serving MME. As a result of the relocation messagingexchange, a transfer is performed (at 506) from the current serving GANCto the target GANC (such as from the GANC 206 to the GANC 208 shown inFIG. 3).

FIG. 6 illustrates an example communications node 600, which can be anyof the nodes depicted in FIGS. 1-3, such as a mobile station, an MME, aGANC, and so forth. The communications node 600 includesmachine-readable instructions 602 executable on a processor (or multipleprocessors) 604. The processor(s) is (are) connected to storage media606 and a communications interface 608. The communications interface 608allows the communications node to communicate with another node. In someexamples, the communications interface 608 is a wireless interface tocommunicate wirelessly with a remote node. Alternatively, thecommunications interface can be a wired interface to communicate over awired connection (e.g., electrical connection, optical connection,etc.).

The machine-readable Instructions 602 are loaded for execution on theprocessor(s) 604. A processor can include a microprocessor,microcontroller, processor module or subsystem, programmable integratedcircuit, programmable gate array, or another control or computingdevice.

Data and instructions are stored in respective storage devices, whichare implemented as one or more computer-readable or machine-readablestorage media. The storage media include different forms of memoryincluding semiconductor memory devices such as dynamic or static randomaccess memories (DRAMs or SRAMs), erasable and programmable read-onlymemories (EPROMs), electrically erasable and programmable read-onlymemories (EEPROMs) and flash memories; magnetic disks such as fixed,floppy and removable disks; other magnetic media including tape; opticalmedia such as compact disks (CDs) or digital video disks (DVDs); orother types of storage devices. Note that the instructions discussedabove can be provided on one computer-readable or machine-readablestorage medium, or alternatively, can be provided on multiplecomputer-readable or machine-readable storage media distributed in alarge system having possibly plural nodes. Such computer-readable ormachine-readable storage medium or media is (are) considered to be partof an article (or article of manufacture). An article or article ofmanufacture can refer to any manufactured single component or multiplecomponents.

In the foregoing description, numerous details are set forth to providean understanding of the subject disclosed herein. However,implementations may be practiced without some or all of these details.Other implementations may include modifications and variations from thedetails discussed above. It is intended that the appended claims coversuch modifications and variations.

What is claimed is:
 1. At least one non-transitory processor-readablemedium carrying instructions for execution by at least one processor ofa first mobility management entity associated with a packet-switchedwireless access network, the instructions comprising: instructionsexecutable by the at least one processor to receive informationassociated with a mobile station being served by the first mobilitymanagement entity, wherein the information identifies a serving genericaccess network controller for the mobile station, the serving genericaccess network controller being used to provide a circuit-switchedservice to the mobile station while the mobile station is attached tothe packet-switched wireless access network; instructions executable bythe at least one processor to initiate a handoff of the mobile stationsfrom the packet-switched wireless access network to a circuit-switchedwireless access network, the circuit-switched wireless access networkbeing in a region served by a second generic access network controllerdifferent from the serving generic access network controller; andinstructions executable by the at least one processor in performing thehandoff to use the information to identify the serving generic accessnetwork controller to communicate handoff-related messaging to theserving generic access network controller to cause provision of thecircuit-switched service to be handed off from the serving genericaccess network controller to the second generic access networkcontroller.
 2. The at least one non-transitory processor-readable mediumof claim 1, wherein the instructions executable by the at least oneprocessor to receive the information comprise instructions executable toreceive the information sent by a home subscriber server for the mobilestation.
 3. The at least one non-transitory processor-readable medium ofclaim 2, wherein the instructions executable to receive the informationcomprise instructions executable to receive the information forwarded bya second mobility management entity to the first nobility managemententity, where the information was sent from the home subscriber serverto the second mobility management entity.
 4. The at least onenon-transitory processor-readable medium of claim 3, wherein theinstructions executable to receive the information by the first mobilitymanagement entity from the second mobility management entity areinstructions executable in response to a transition of the mobilestation from the second mobility management entity to the first mobilitymanagement entity.
 5. The at least one non-transitory processor-readablemedium of claim 1, wherein the instructions executable to receive theinformation comprise instructions executable to receive the informationprovided in response to an authentication procedure performed by themobile station in connection with a registration procedure performed bythe mobile station with the serving generic access network controller.6. The at least one non-transitory processor-readable medium of claim 1,wherein the instructions executable to initiate the handoff to thecircuit-switched wireless access network comprise instructionsexecutable to initiate the handoff to the circuit-switched wirelessaccess network in which the mobile station is provided with thecircuit-switched service via the circuit-switched wireless accessnetwork instead of via the packet-switched wireless access network. 7.The at least one non-transitory processor-readable medium of claim 1,for use in a mobility management entity in a packet-switched wirelessaccess network which is an EUTRA (Evolved Universal Terrestrial RadioAccess) network.
 8. The at least one non-transitory processor-readablemedium of claim 1, wherein the information identifies a serving genericaccess network controller for the mobile station, the serving genericaccess network controller being used to provide a circuit-switched voiceservice to the mobile station while the mobile station is attached tothe packet-switched wireless access network.
 9. At least onenon-transitory processor-readable medium carrying instructions forexecution by at least one processor of a mobile station, theinstructions comprising: instructions executable by the at least oneprocessor to perform, in a mobile station, a registration procedure witha serving generic access network controller; instructions executable bythe at least one processor to perform an authentication procedure inconnection with the registration procedure, the authentication procedurecausing an identity of the serving generic access network controller tobe provided to a home subscriber server of the mobile station; andinstructions executable by the at least one processor to perform ahandoff from a packet-switched domain to a circuit-switched domain, themobile station being provided with a circuit-switched service whileattached to the packet-switched domain, and the mobile stationcontinuing to be provided with the circuit-switched service afterhandoff to the circuit-switched domain, and the handoff involving anentity in the packet-switched domain using the identity of the servinggeneric access network controller to send a relocation request to theserving generic access network controller to cause handoff from theserving generic access network controller to a target generic accessnetwork controller.
 10. The at least one non-transitoryprocessor-readable medium of claim 9, wherein the instructions furthercomprise instructions executable by the at least processor to detectmovement of the mobile station that satisfies a predefined criterion,wherein the instructions executable to perform the registrationprocedure and the authentication procedure are executed in response odetecting the movement that satisfies a predefined criterion.
 11. The atleast one non-transitory processor-readable medium of claim 9, for usein a mobile station in an EUTRA (Evolved Universal Terrestrial RadioAccess) domain.